The objective of this study is to augment the genetic quality assurance program of biochemical analysis of markers with the more definitive DNA fingerprinting technique. This molecular biological tool is indispensable for resolving ambiguous data. The application of the DNA fingerprinting technique will permit greater precision in detecting genetic contamination and mutation by discovering differences between closely related strain, substrains and congenic rats and mice. Tissue samples from tail and livers of various inbred and congenic strains of rats and mice have been processed to purify DNA. Preliminary studies indicate that both the liver and tail tissues provide DNA of the same sensitivity. Ultimately, DNA fingerprint profiles will be available for all animals tested in this facility and attempts will be made to correlate DNA fingerprint profiles with genetic change.